Nucleic Acids

Nucleic acids are polymers of nucleotides — molecules made up of a pentose sugar, a nitrogen-containing base, and a phosphate group.

There are two types of nucleic acids: Deoxyribonucleic acid, or DNA, and ribonucleic acid, or RNA. Their chemical structures differ based on the pentose sugar and nitrogenous bases they contain.

The pentose sugar in RNA is ribose, which has a hydroxyl group attached to carbon-2. The sugar in DNA is deoxyribose, which has a hydrogen atom instead of a hydroxyl group at carbon-2. The nitrogenous base is bonded to carbon-1 of the sugar, while the phosphate group is attached to carbon-5.

Both RNA and DNA contain the bases adenine, cytosine, and guanine. But DNA contains thymine, while RNA contains uracil.

These bases are grouped into two categories: purines and pyrimidines. Adenine and guanine are purines with a double-ring structure, while the other bases are pyrimidines with a single-ring structure.

In DNA and RNA, guanine and cytosine form complementary base pairs, linked by three hydrogen bonds. Adenine and thymine form base pairs in DNA, while in RNA, adenine and uracil pair together. Both pairs are linked by two hydrogen bonds.

DNA and RNA polymerase enzymes catalyze the formation of nucleic acid chains by linking nucleotides together.

A phosphodiester bond forms between the hydroxyl group attached to carbon-3 of one nucleotide and the phosphate group attached to carbon-5 of the next nucleotide. This reaction leaves a free phosphate group at the five-prime end and a free hydroxyl group at the three-prime end.

When paired with a complementary strand, the two molecules are antiparallel, meaning one strand runs five prime to three prime, while the complementary strand runs three prime to five prime.

The strands are held together by several intermolecular forces, including hydrogen bonds between bases, hydrophobic effects, and van der Waals interactions between stacked bases.

DNA is a double helix made up of two polynucleotide chains wound around each other. In contrast, RNA is often found as a single-stranded molecule.

However, RNA can bind to a complementary RNA or DNA strand. It can also form intra-strand complementary base pairs, resulting in different RNA secondary structures that have distinct functions within the cell.